THE MEDIA BUSINESS: ADVERTISING; A Warning in Expanding Waistlines

The Big Mac. Kraft Lunchables. Pizza Hut's six-cheese Insider pizza. These and other artery-choking products represent the American food industry's mastery of the art of selling high-fat, high-calorie food.

But now, with the nation's waistline stretched beyond belief, some food companies are recasting themselves as good corporate citizens alarmed at the rate of obesity in the United States and willing to modify their offerings to help avert a looming health care crisis.

McDonald's and the Frito-Lay division of PepsiCo plan to remove saturated fats and trans fatty acids from french fries, chips and other products because of concerns about their link to high cholesterol, heart disease and diabetes.

Kraft Foods, which makes Oreo cookies, Velveeta cheese and Oscar Mayer cold cuts, said last week that it planned to reduce portion sizes and cut the fat and sugar content of many products. The company also said it would stop marketing its products in schools.

But some consumer advocates and health experts are skeptical. They doubt that companies that have profited, and helped create, a culture of overeating, particularly among children, can be trusted to help put America on a diet.

''Are they going to pull back some of this marketing to children?'' asked Margo Wootan, a nutritionist at the Center for Science in the Public Interest, a consumer advocacy group. ''We'll see. Their marketing aimed at kids is terrible. And it has increased. They bypass the parents and go directly to kids. They make parents have to say no all the time.''

Many food companies, of course, have long marketed low calorie or low-fat foods. What is new in the companies' latest moves is their pledge to take steps aimed at moderating consumption of their core and often most profitable products -- the tasty, fatty, salty or sugary fare that consumers seem unable to resist.

The shift comes at a time when food companies are under growing pressure to do something about the obesity epidemic. Class-action lawyers are focusing on food makers with much the same fervor they used to have when going after the tobacco industry.

Lawmakers and regulators in the United States and Europe are also threatening to crack down on food makers by adopting new labeling and marketing restrictions.

In Sweden, for instance, advertising aimed at children under 12 has been banned. And the New York City public schools recently announced a ban on soda, candy and other sugary snacks from school vending machines to address obesity in children. Yesterday, the federal Food and Drug Administration announced that food labels would have to list levels of trans fatty acids by 2006.

Kraft's moves appear bold for the industry. But some consumer advocates point out that Kraft is majority owned by the tobacco giant Altria, formerly known as Philip Morris, which has been harshly criticized and even sued for the way it marketed its tobacco products.

''Kraft is playing good citizen,' said John McMillin, a food industry analyst at Prudential Securities. ''Altria, their majority owner, has been through this in tobacco. And they don't want to wait till something happens to them.''

''There is a clear long-term risk to producers of fast foods, soft drinks, confectionery and snacks that anti-obesity measures will curb their ability to grow revenues in the future,'' Jason Streets, an analyst at UBS, wrote in a report issued in November. ''We believe there are risks associated with obesity that have not yet been factored into share prices.''

UBS recently issued a report that ranked large companies with the highest percentage of unhealthy, or ''less good food'' offerings, and Hershey, McDonald's, Coca-Cola and Nestlé were ranked Nos. 1, 2, 7 and 10 respectively on the obesity index. While hardly a scientific study, the report suggests that Wall Street is at least handicapping the effect that the public health debate could have on the corporate bottom line.

The number of obese people in the United States has more than doubled since 1980, and is near 50 million, according to the Centers for Disease Control and Prevention. And there are estimates that obesity-related problems cost the nation about $70 billion a year, reported the International Obesity Task Force in London.

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The World Health Organization, which recently called obesity a worldwide epidemic, is pressing food companies to change their product lineups and tame their marketing to children.

But the industry has been reluctant to take the blame for the nation's health problems. Executives in the industry like to attribute the soaring obesity rates to a lack of exercise and the increasingly sedentary lifestyle of so many Americans, in addition to poor eating choices.

''I wouldn't say we're part of the problem,'' said Steven Anderson, president of the National Restaurant Association, which represents big outlets like McDonald's and Burger King, as well as thousands of other restaurants. ''There are not good or bad foods. There are good and bad diets. This does come down to personal responsibility.'

Indeed, most big food companies do not even like to talk about selling ''unhealthy foods.'' And they don't like to use the words junk food.

Nestlé, the world's biggest food company, calls itself a nutrition company, citing its growing number of diet products rather than its popular chocolates. (Nestlé owns the Lean Cuisine brand.) Coca-Cola executives point out that the company also sells Minute Maid orange juice. And McDonald's executives insist that their foods are healthy.

''To make a general statement that McDonald's food is unhealthy is wrong,'' says Ken Barun, vice president for the healthy lifestyles initiative at McDonald's. ''We've got salads, hamburgers, yogurt. The choices there can fit into any diet.''

On paper, health experts say, Kraft is going where no other major food company has gone before by saying it will do something to control how much fat and sugar its customers take in.

Yet Kraft executives are not promising anything drastic. Many of the changes are expected to be small, and some could take years to put in place, the company says.

''We're not going to do anything radical,'' said a Kraft spokesman, Michael Mudd. ''This is about making incremental changes across a broad base of our most popular products. We don't want to lose the tastes that people have come to love.''

But that leads to the question: What exactly can food makers do to fight obesity?

''I'd tell them to market smaller portion sizes, don't glorify overeating and lay off children; that would be my top three,'' said Kelly D. Brownell, a Yale professor who heads the university's Center for Eating and Weight Disorders.

Marion Nestle, a professor of nutrition at New York University and a longtime critic of big food companies, was skeptical.

Asked what Kraft could do to fight obesity, she said succinctly, ''Stop making junk food.'' Then she added: ''People don't have to eat these foods. I want people eating real foods, produced by local farmers. I'm hopelessly idealistic.''

If the obesity problem is going to be solved, health experts say, Americans are going to have to make better choices, and marketers are going to have to stop themselves from ''super-sizing'' everything.

The extent to which overindulgence has seeped into American culture was summed up by a flight attendant on a Southwest Airlines flight from Providence, R.I., to Chicago on Monday. ''Having a balanced diet,'' she told the passengers over the intercom, ''means having two cookies in each hand.''